Problem with the last \foreach of this code : won't compile

Question

\documentclass{article}
\usepackage{tikz}
\usepackage{pgfmath}
\usetikzlibrary{calc,intersections,through,backgrounds}

\begin{document}


\begin{tikzpicture}[scale=2]
\draw[step=5mm, gray, very thin] (-4,-4) grid (4,4) ;
\draw[thin, blue] (-3,0) -- (3,0) ;
\draw[thin, blue] (0,-3) -- (0,3) ;

\draw (2.5,0) -- (1.5,2) -- (0,0);
\draw[dotted] (1.5,1) -- (1.5,2) ;
\draw[dotted] (0,0) -- (1.5,1) ;
\draw (0,0) -- (-0.5,1.5) -- (1.5,2) ;
\draw (0,0) -- (2,-1) -- (2.5,0) ;
\draw[dashed] (0,0) -- (2.5,0) ;
\draw (2,-1) -- (1.5,2) ;
\draw (0,0) -- (0.5,-1) -- (2,-1) ;
\path [name path = ligne1] (0.5,-1) -- (2.5,0) ;
\path [name path = ligne2] (0,0) -- (2,-1) ;
\path [name intersections={of= ligne1 and ligne2, by={ x12 }}];
\draw[dashed] (0.5,-1) -- (x12) ;
\draw[dotted] (x12) -- (2.5,0) ;
\path [name path = ligne3] (1.5,1) -- (0.5,-1) ;
\path [name intersections={of= ligne2 and ligne3, by={ x23 }}];
\draw[dashed] (0.5,-1) -- (x23) ;
\draw[dotted] (x23) -- (1.5,1) ;
\draw (-0.5,1.5) -- (-0.5,0.25) -- (0.5,-1) ;
\path [name path = ligne4] (-0.5,0.25) -- (1.5,1) ;
\path [name path = ligne5] (0,0) -- (-0.5,1.5) ;
\path [name path = ligne6] (0,0) -- (1.5,2) ;
\path [name intersections={of= ligne4 and ligne5, by={ x45 }}];
\path [name intersections={of= ligne4 and ligne6, by={ x46 }}];
\draw[dashed] (-0.5,0.25) -- (x45) ;
\draw[dashed] (x45) -- (x46)(1.5,1) ;
\draw[dotted] (x46) -- (1.5,1) ;
\draw (0,0) -- (-0.5,0.25) ;
\path [name path = ligne7] (2,-1) -- (1.5,2) ;
\path [name path = ligne8] (2.5,0) -- (1.5,1) ;
\path [name intersections={of= ligne7 and ligne8, by={ x78 }}];
\draw[dotted] (2.5,0) -- (x78) ;
\draw[dotted ] (x78) -- (1.5,1) ;
\path [name path = ligne9] (-0.5,1.5) -- (1.5,1) ;
\path [name intersections={of= ligne6 and ligne9, by={ x69 }}];
\draw[dashed] (-0.5,1.5) -- (x69) ;
\draw[dotted] (x69) -- (1.5,1) ;
\path [name path = ligne10] (0,0) -- (2.5,0) ;
\path [name path=cercle1] (0,0) circle [radius = 1] ;
\path [name intersections={of= ligne10 and cercle1, by={ a }}];
\path [name intersections={of= ligne6 and cercle1, by={ b }}];
\path [name path = ligne11] (2.5,0) -- (1.5,2) ;

\foreach \n in {0,1,2,3,4,5,6,7,8,9,10}
    {\path [name path = div1\n] (0,0) -- ({2.5 -(1*\n)/10},{(2*\n)/10}) ;
     \path [name intersections={of= cercle1 and div1\n, by={ a\n }}] ;


        } ;

\draw[blue,smooth, name path = arca] plot coordinates {(a0) (a1) (a2) (a3) (a4) (a5) (a6) (a7) (a8) (a9) (a10)} ;

\path[name path = cercle2] (0,0) circle [x radius = 1cm, y radius =0.4cm] ;
\foreach \n in {0,1,2,3,4,5,6,7,8,9,10}
{\path [name path = div2\n] (0,0) -- ({2.5 -(1*\n)/10},{(1*\n)/10}) ;
    \path [name intersections={of= cercle2 and div2\n, by={ b\n }}] ;
} ;
\draw[green,smooth, name path = arcb] plot coordinates {(b0) (b1) (b2) (b3) (b4) (b5) (b6) (b7) (b8) (b9) (b10)} ;

\path [name path=prearcc] (a10) -- (b10) ;
\coordinate (c) at ($(a10)!0.5!(b10)$) ;


\draw [name path = cercle3]
      let \p1 = ($ (a10) - (c) $),
          \n2 = {veclen(\x1,\y1)}
      in
          (c) circle [x radius = 0.25mm, y radius = \n2,rotate = -11]    ;


\coordinate (c') at ($(a10) - (b10)$) ;
\coordinate (c'') at ($0.1*(c')$) ;


\foreach \i in {0,1,2,3,4,5,6,7,8,9,10}
{\path [draw,red,name path = divnew\i] (c) -- ($ { \i * (c'')} $) ;
    \path [name intersections={of= cercle3 and divnew\i, by={ c\i }}] ;
} ;

\end{tikzpicture}
\end{document}

Hello everybody ! If someone could halp me with the last lines (last \foreach) of this code... It causes the compilation to stop... I've been trying to fox it for hours... Thanks to anyone who may help : ) — MarcelBenard, Aug 07 '16 at 15:08
I haven't tested but looks like you have no intersections if that's the error location — percusse, Aug 07 '16 at 15:27
You wrote ($0.1*(c')$) with no accident, so remove {} in (${\i*(c'')}$) — Symbol 1, Aug 07 '16 at 15:57
Thanks very much for your help. I found a solution. Indeed, I removed the {}, and, also, it seems that leaving spaces in ($ { \i * (c'')} $) (between\i and * and (c'')) was seen as an when compiling. — MarcelBenard, Aug 07 '16 at 21:18

score 3 · Answer 1 · edited Apr 13 '17 at 12:35

I feel nervous to comment something but... just to enrich this answer.

In the first course of TeX we are taught that if anything gets wrong, add braces. For instance $10^10$ . However TikZ works in another way. As @percusse explained in this answer, the core of TikZ repeatedly check the next character and decide what to do next. It will not work if it meets useless braces. So that is the first lesson: add no braces unless necessary.

Then, TikZ uses a TeX feature to check your spelling. Borrowing @percusse's example:

def\tikz@collect@coordinate@onpath@#1oordinate{%
  \pgfutil@ifnextchar[{\tikz@@collect@coordinate@opt#1}{\tikz@@collect@coordinate@opt#1[]}}%}

Similarly, in tikzlibrarycalc.code.tex it defines:

\def\tikz@cc@parse@factor#1*({%
  \pgfmathparse{#1*\tikz@cc@factor}%
  \let\tikz@cc@factor=\pgfmathresult%
  \tikz@cc@coordinate(%)
}

So that is the second lesson: add no spaces unless necessary.

Problem with the last \foreach of this code : won't compile

1 Answers1